LibWeb/CSS: Parse and propagate the font-language-override property

Author: https://github.com/AtkinsSJ
Commit: https://github.com/LadybirdBrowser/ladybird/commit/1d8867d9ae9
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1554

Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt

@@ -11,6 +11,7 @@ fill: rgb(0, 0, 0)
 fill-opacity: 1
 fill-rule: nonzero
 font-family: serif
+font-language-override: normal
 font-size: 16px
 font-style: normal
 font-variant: normal
@@ -116,7 +117,7 @@ grid-row-start: auto
 grid-template-areas: 
 grid-template-columns: 
 grid-template-rows: 
-height: 2006px
+height: 2023px
 inline-size: auto
 inset-block-end: auto
 inset-block-start: auto

Userland/Libraries/LibWeb/CSS/ComputedValues.h

@@ -485,6 +485,7 @@ public:
     CSSPixels font_size() const { return m_inherited.font_size; }
     int font_weight() const { return m_inherited.font_weight; }
     CSS::FontVariant font_variant() const { return m_inherited.font_variant; }
+    Optional<FlyString> font_language_override() const { return m_inherited.font_language_override; }
     CSSPixels line_height() const { return m_inherited.line_height; }
     CSS::Time transition_delay() const { return m_noninherited.transition_delay; }
 
@@ -516,6 +517,7 @@ protected:
         CSSPixels font_size { InitialValues::font_size() };
         int font_weight { InitialValues::font_weight() };
         CSS::FontVariant font_variant { InitialValues::font_variant() };
+        Optional<FlyString> font_language_override;
         CSSPixels line_height { InitialValues::line_height() };
         CSS::BorderCollapse border_collapse { InitialValues::border_collapse() };
         CSS::Length border_spacing_horizontal { InitialValues::border_spacing() };
@@ -672,6 +674,7 @@ public:
     void set_font_size(CSSPixels font_size) { m_inherited.font_size = font_size; }
     void set_font_weight(int font_weight) { m_inherited.font_weight = font_weight; }
     void set_font_variant(CSS::FontVariant font_variant) { m_inherited.font_variant = font_variant; }
+    void set_font_language_override(Optional<FlyString> font_language_override) { m_inherited.font_language_override = font_language_override; }
     void set_line_height(CSSPixels line_height) { m_inherited.line_height = line_height; }
     void set_border_spacing_horizontal(CSS::Length border_spacing_horizontal) { m_inherited.border_spacing_horizontal = border_spacing_horizontal; }
     void set_border_spacing_vertical(CSS::Length border_spacing_vertical) { m_inherited.border_spacing_vertical = border_spacing_vertical; }

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -5447,6 +5447,51 @@ RefPtr<CSSStyleValue> Parser::parse_font_family_value(TokenStream<ComponentValue
     return StyleValueList::create(move(font_families), StyleValueList::Separator::Comma);
 }
 
+RefPtr<CSSStyleValue> Parser::parse_font_language_override_value(TokenStream<ComponentValue>& tokens)
+{
+    // https://drafts.csswg.org/css-fonts/#propdef-font-language-override
+    // This is `normal | <string>` but with the constraint that the string has to be 4 characters long:
+    // Shorter strings are right-padded with spaces, and longer strings are invalid.
+
+    {
+        auto transaction = tokens.begin_transaction();
+        tokens.skip_whitespace();
+        if (auto keyword = parse_keyword_value(tokens); keyword->to_keyword() == Keyword::Normal) {
+            tokens.skip_whitespace();
+            if (tokens.has_next_token()) {
+                dbgln_if(CSS_PARSER_DEBUG, "CSSParser: Failed to parse font-language-override: unexpected trailing tokens");
+                return nullptr;
+            }
+            transaction.commit();
+            return keyword;
+        }
+    }
+
+    {
+        auto transaction = tokens.begin_transaction();
+        tokens.skip_whitespace();
+        if (auto string = parse_string_value(tokens)) {
+            auto string_value = string->as_string().string_value();
+            tokens.skip_whitespace();
+            if (tokens.has_next_token()) {
+                dbgln_if(CSS_PARSER_DEBUG, "CSSParser: Failed to parse font-language-override: unexpected trailing tokens");
+                return nullptr;
+            }
+            auto length = string_value.code_points().length();
+            if (length > 4) {
+                dbgln_if(CSS_PARSER_DEBUG, "CSSParser: Failed to parse font-language-override: <string> value \"{}\" is too long", string_value);
+                return nullptr;
+            }
+            transaction.commit();
+            if (length < 4)
+                return StringStyleValue::create(MUST(String::formatted("{<4}", string_value)));
+            return string;
+        }
+    }
+
+    return nullptr;
+}
+
 JS::GCPtr<CSSFontFaceRule> Parser::parse_font_face_rule(TokenStream<ComponentValue>& tokens)
 {
     auto declarations_and_at_rules = parse_a_list_of_declarations(tokens);
@@ -7528,6 +7573,10 @@ Parser::ParseErrorOr<NonnullRefPtr<CSSStyleValue>> Parser::parse_css_value(Prope
         if (auto parsed_value = parse_font_family_value(tokens); parsed_value && !tokens.has_next_token())
             return parsed_value.release_nonnull();
         return ParseError::SyntaxError;
+    case PropertyID::FontLanguageOverride:
+        if (auto parsed_value = parse_font_language_override_value(tokens); parsed_value && !tokens.has_next_token())
+            return parsed_value.release_nonnull();
+        return ParseError::SyntaxError;
     case PropertyID::GridArea:
         if (auto parsed_value = parse_grid_area_shorthand_value(tokens); parsed_value && !tokens.has_next_token())
             return parsed_value.release_nonnull();

Userland/Libraries/LibWeb/CSS/Parser/Parser.h

@@ -305,6 +305,7 @@ private:
     RefPtr<CSSStyleValue> parse_flex_flow_value(TokenStream<ComponentValue>&);
     RefPtr<CSSStyleValue> parse_font_value(TokenStream<ComponentValue>&);
     RefPtr<CSSStyleValue> parse_font_family_value(TokenStream<ComponentValue>&);
+    RefPtr<CSSStyleValue> parse_font_language_override_value(TokenStream<ComponentValue>&);
     RefPtr<CSSStyleValue> parse_list_style_value(TokenStream<ComponentValue>&);
     RefPtr<CSSStyleValue> parse_math_depth_value(TokenStream<ComponentValue>&);
     RefPtr<CSSStyleValue> parse_overflow_value(TokenStream<ComponentValue>&);

Userland/Libraries/LibWeb/CSS/Properties.json

@@ -1145,6 +1145,7 @@
   "font": {
     "inherited": true,
     "initial": "normal medium serif",
+    "__comment": "FIXME: Handle properties that are reset implicitly. https://drafts.csswg.org/css-fonts/#reset-implicitly",
     "longhands": [
       "font-family",
       "font-size",
@@ -1164,6 +1165,17 @@
       "string"
     ]
   },
+  "font-language-override": {
+    "animation-type": "discrete",
+    "inherited": true,
+    "initial": "normal",
+    "valid-types": [
+      "string"
+    ],
+    "valid-identifiers": [
+      "normal"
+    ]
+  },
   "font-size": {
     "animation-type": "by-computed-value",
     "inherited": true,

Userland/Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -1000,6 +1000,14 @@ Optional<CSS::FontVariant> StyleProperties::font_variant() const
     return keyword_to_font_variant(value->to_keyword());
 }
 
+Optional<FlyString> StyleProperties::font_language_override() const
+{
+    auto value = property(CSS::PropertyID::FontLanguageOverride);
+    if (value->is_string())
+        return value->as_string().string_value();
+    return {};
+}
+
 CSS::GridTrackSizeList StyleProperties::grid_auto_columns() const
 {
     auto value = property(CSS::PropertyID::GridAutoColumns);

Userland/Libraries/LibWeb/CSS/StyleProperties.h

@@ -147,6 +147,7 @@ public:
     Optional<CSS::PointerEvents> pointer_events() const;
     Variant<CSS::VerticalAlign, CSS::LengthPercentage> vertical_align() const;
     Optional<CSS::FontVariant> font_variant() const;
+    Optional<FlyString> font_language_override() const;
     CSS::GridTrackSizeList grid_auto_columns() const;
     CSS::GridTrackSizeList grid_auto_rows() const;
     CSS::GridTrackSizeList grid_template_columns() const;

Userland/Libraries/LibWeb/Layout/Node.cpp

@@ -469,8 +469,9 @@ void NodeWithStyle::apply_style(const CSS::StyleProperties& computed_style)
 
     if (auto maybe_font_variant = computed_style.font_variant(); maybe_font_variant.has_value())
         computed_values.set_font_variant(maybe_font_variant.release_value());
+    if (auto maybe_font_language_override = computed_style.font_language_override(); maybe_font_language_override.has_value())
+        computed_values.set_font_language_override(maybe_font_language_override.release_value());
 
-    // FIXME: BorderXRadius properties are now BorderRadiusStyleValues, so make use of that.
     auto border_bottom_left_radius = computed_style.property(CSS::PropertyID::BorderBottomLeftRadius);
     if (border_bottom_left_radius->is_border_radius()) {
         computed_values.set_border_bottom_left_radius(